Chondracanthus
exasperatus iridescence

The iridescence of some of the red algae, including C.
exasperatus, is one of the most aesthetically beautiful characteristics
associated with any alga. If you have not been fortunate enough to see
it for yourself scuba diving or at an aquarium, iridescence on the thalli of
the reds is similar to the dancing blues, green,
and reds of light reflecting
off soap bubbles. It is most brilliant underwater, and truly one of the
more amazing sites in the phycology world.

Iridescence is one of the most
easily recognizable characteristics of algae, and hence commonly
used for taxonomic classification. However, the mechanisms behind
iridescence for most algae is not well understood. Two different
mechanisms have already been discovered to be behind the phenomena
of iridescence. Iridescent
bodies have been identified as the source of iridescence in Chondria and Gastroclonium,
while in Iridaea it has been identified as a multi-layered cuticle
(Lee, 1980).